Worried you’ll outgrow the cloud? You’re not alone.

If you think about it, Netflix’s metamorphosis into a company that runs its infrastructure completely atop cloud-based resources is truly remarkable. It’s a very large company with a very large IT operation and, presumably, a rather large bill in the mail every month from Amazon Web Services. Engineering effort aside, the fact that Netflix has decided it’s worth it to pay the cloud computing premium is the most amazing part. With many companies, the bigger they get, the faster they come down from the clouds.

Case in point: Yottaa. The web-optimization startup, which also launched its own CDN service in March, is transitioning its network into a hybrid model of cloud-based and physical servers after launching in the cloud exclusively. It’s a significant shift considering the company was actually a finalist in the 2010 Amazon Web Services Start-Up Challenge and touted its cloud-based approach when the company launched last April.

Don’t get me wrong, the cloud-only model has served Yottaa well. Its network is actually spread across multiple providers, including AWS, Microsoft and Voxel, and that distribution helped the company reroute traffic to avoid any major downtime during last year’s four-day AWS outage. And even as it moves to a hybrid model, the cloud still has benefits. “We can literally scale to hundreds of thousands of machines in a matter of hours,” said Yottaa Founder and CEO Coach Wei.

As the company grew, however, cost, performance and security issues meant Yottaa had to decrease its cloud dependency:

Cost: According Wei, it’s easy to get started in the cloud — you can spin up only as many servers as you need at any given time and don’t have to invest in 100,000 physical servers to match Akamai’s architecture — but “when you get to a certain scale, it’s actually not cost-effective anymore.” For Yottaa, which is serving 100 million unique visitors across its network every month for more than 80,000 web sites, that time has already come. Actually, Wei said, Yottaa always planned to move to a hybrid architecture, but even still he was surprised at how much the cloud could cost. Before he started Yottaa, he’d never thought about paying a million dollars a year to AWS.

Performance: The performance trade-offs in the cloud can be problematic, too. Wei said network performance is the biggest problem for Yottaa, as it’s typically about 50 percent slower in the cloud and variable at that. You never know what type of performance you’ll get at any given time. If someone else is using a lot of bandwidth, your service might suffer. And while some cloud providers throttle bandwidth at 100 Mbps per user, Wei said, “at the high end of the scale, that’s just way too low.”

Security: Wei notes all sorts of security problems with cloud computing, but the major one is the inability to use tried-and-true physical appliances for security. Not only do physical appliances provide a lot in terms of traffic-monitoring and load-balancing, but they can store thousands of IP addresses for SSL certificates on a single box. A cloud provider, Wei said, might only give you a handful of IP addresses.

With its new hybrid model, Yottaa still leverages the cloud when necessary — like when it would be faster serving an Australian end-user through a cloud provider there than a physical server in the United States — but it targets physical resources whenever possible. Its network now includes cloud and/or physical servers in 24 cities across the globe.

Of course, for every company (or several companies) that decides to switch from a cloud-centric architecture, there’s a Netflix or Animoto that decides to stay all in the cloud. It’s really a matter of knowing what’s best for your business. We’ll talk all about ideal infrastructure choices at our Structure conference in June, which includes top executives from Zynga, Amazon and Netflix among others.